Based on what little I've seen and all the accounts of his play, Bill Russell was. Since I don't have enough evidence I've seen myself to pick him for sure, I'd say Pippen was the best all around defender I've ever seen. He did just about everything.

In terms of ATG players the guys who are top 10 at their position are usually defensive beasts as well, but then you have to consider defensive guys like Mutombo and Rodman. Even guys like Bruce Bowen and Sidney Moncrief might deserve a shake. Olajuwon was an all-around beast so he is deserving on accolades and rank alone, but was he really the "best". Tim Duncan might say otherwise.

In terms of ATG players the guys who are top 10 at their position are usually defensive beasts as well, but then you have to consider defensive guys like Mutombo and Rodman. Even guys like Bruce Bowen and Sidney Moncrief might deserve a shake. Olajuwon was an all-around beast so he is deserving on accolades and rank alone, but was he really the "best". Tim Duncan might say otherwise.